Theorem 2.26: 
([1]})
Let \((M,I)\)  be a hyperkähler manifold, and \(W\) 
a connected component of its birational
moduli space. Then \(W\)  is isomorphic to \({\operatorname{{P}\sf er}}/\Gamma \) ,
where \(\Gamma \)  is
an arithmetic subgroup in \(O(H^2(M, {R}), q)\) , called the
monodromy group of \((M,I)\) . In fact \(\Gamma \)  is the image of \(\widetilde{\Gamma }\) 
in \(O(H^2(M, {R}), q)\) .

